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musings on dynamic properties of barreled arrows

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Del the cat:
I think it's all very fine margins...my mate JT shot one of my flight ELBs on Sunday, very hot, head wind... about 50 yards short >:( , yet he was getting back a full draw where last time he was short drawing.
It's very hard to change one variable without effecting the others.
Im sure we are all shooting barrelled arrows and just an extra 0.2mm diameter in the middle can add stiffness, but o you taper sharply at the ends and leave a good few inches in the middle fatter or tape all the way up to the thickest point?
It's all very subtle. Fat at the back gives a poor FOC... or is it poor? Hickman says you want 10% FOC but the Turkish arrows are behind centre. Do you need more mass and more FOC in a head wind?
So many questions... hopefully a bit of variation in the arrows and I may stumble across the best match to the bow.
I've just made one a whisker fatter in the middle but more tapered at the ends so it's prob dynamically stiffer, I've got the balance point about 1.5" front of centre... weighed it and the scale read 190 gn!!! :o   My instincts kicked in and I though... that can't be right!! So I got another flight arrow and weighed that 275gn... re-weighed the new one 260gn, that's more believable.
Maybe I hadn't let the scale zero. ::)
Prob' with an ELB flight bow is the width at the grip.... just how low a brace dare I go for max powerstroke without risking snapped arrows?
That's what keep us playin' this game  :)
Del

JNystrom:
Good choice is just to make as many different weight/spine/balance point arrows that you possibly can and you will find a good one from the lot. But who am i to give you tips, you Del are still a lot of ahead of me in distance. I'm coming!  (lol) (SH)

Assuming your arrow is somewhere around 28-30" and for a 80+ pound bow, even 260gn is really light. But i'm not sure, i myself have been shooting too stiff arrows for a while! Hah.

willie:

--- Quote from: JNystrom on May 07, 2018, 04:28:21 am ---If oscillation is what we want to improve, shouldn't the optimal shape be symmetrical? In other words, pile and nock end equally tapered and balance point in middle.

--- End quote ---

Do we want to improve the oscillations or eliminate it?   I am hoping that reducing or canceling the vibrations created at release will let the arrow fly straighter and further.

Del the cat:
@ Willie.
There will always be oscillation (especially with an ELB where the arrow has to flex round the bow more than a bow with a cut away shelf).
I think we need to help the oscillation to be as small as is feasible and to die down as quickly as possible.
As usual improving one property often worsens another  >:(
Mind that's more easily said than done...
Maybe a tubular arrow with the hole down the middle filled with porridge or molasses would damp out the vibration  ::)
If it didn't work you could always snack on it  :)
Del

willie:
Del,
of course the flex is needed at the loose unless centershot, but how to best settle the arrow after it clears the bow is the question. Joachim noted in the opening post that more mass in the ends seems detrimental to quick reduction. He also postulated that....

--- Quote ---My gut feeling tells me we need arrows that bend evenly when spined, in a slightly elliptical tiller shape. This should give higher frequency oscillations that return more quickly to a static shape, even at rather low static spine weights.
--- End quote ---

I agree that higher freq vibes can be attenuated easier. A question in my mind is, can an assymetrical bend set up a tendency for two different harmonics to hopefully self cancel faster?

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